This phase II/III trial tests the role of DNA released from tumor cells into the blood in guiding the use of immunotherapy (nivolumab alone or with relatlimab) after surgical removal of the bladder for bladder cancer treatment. DNA is material found inside all of our cells that acts as a blueprint for how cells function. Tumor cells often have abnormal DNA that looks different than DNA in normal cells. A new test called Signatera has been developed that can detect bladder cancer DNA in the blood which might indicate the presence of bladder tumor cells somewhere in the body. Immunotherapy with monoclonal antibodies, such as nivolumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Relatlimab is a monoclonal antibody that may interfere with the ability of tumor cells to grow and spread. This trial may help doctors determine if the Signatera test can better identify which patients need an additional treatment with immunotherapy to help prevent bladder cancer from coming back after surgery.

This phase II trial compares the use of pembrolizumab and radiation therapy to chemotherapy with cisplatin, gemcitabine, 5-fluorouracil or mitomycin-C and radiation therapy for the treatment of patients with non-muscle invasive bladder cancer. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Chemotherapy drugs, such as cisplatin, gemcitabine, 5-fluorouracil or mitomycin-C, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Radiation therapy uses high energy x-rays, particles, or radioactive seeds to kill cancer cells and shrink tumors. Giving pembrolizumab with radiation may kill more tumor cells than chemotherapy with radiation therapy in patients with non-muscle invasive bladder cancer.

This phase III trial compares the effect of shorter term radiation (ultra-hypofractionated) therapy to the usual radiation therapy (hypofractionation) with standard of care chemotherapy, with cisplatin, gemcitabine or mitomycin and 5-fluorouracil for the treatment of patients with muscle invasive bladder cancer. Giving ultra-hypofractionated radiation may be equally effective as hypofractionated therapy for patients with muscle invasive bladder cancer.

This phase II trial tests the effect of giving pembrolizumab in combination with radiation therapy after chemotherapy in preventing surgery to remove the bladder in patients with muscle invasive bladder cancer. Giving pembrolizumab in combination with radiation therapy after neoadjuvant chemotherapy may help prevent surgical removal of the bladder in patients with muscle invasive bladder cancer.